Carb. experts (Lars) need some help!
Thread Starter
Pro
Joined: May 2001
Posts: 524
Likes: 59
From: watchung N.J.
Carb. experts (Lars) need some help!
I am running a fresh 355 c.i. w/ 10.5 comp. comp cams XS-262 solid cam (224 in.230 ex. 477lift in. 488 lift ex. @.50, World sportsman II heads w/202 intake valves, early Lt-1 dual plane alum. intake, headers, H.E.I., 38 total advance 14 initial, 2000 stall conv., th-400, 3:08 in rear.
My problem is that with my new Holley 700 dbl,pumper I can't get consistent
sparkplug readings, some are sooty, others are tan, when I switch to the old 600 cfm vac. sec. that was sitting in the barn for the last 16 years they all burn tan. no one at Holley seems to know, I thought
someone here might, I really like the performance from the 700, but why w'ont the plugs read right?
Thanks SPOKE-
My problem is that with my new Holley 700 dbl,pumper I can't get consistent
sparkplug readings, some are sooty, others are tan, when I switch to the old 600 cfm vac. sec. that was sitting in the barn for the last 16 years they all burn tan. no one at Holley seems to know, I thought
someone here might, I really like the performance from the 700, but why w'ont the plugs read right?
Thanks SPOKE-
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
Cruise-In I Veteran
Cruise-In II Veteran
Re: Carb. experts (Lars) need some help! (spokewrench)
are you making your plug read after a full throttle run with a clean cut off,push in the clutch and turn of the ignition? DP are very rich on the idle curcuit and if you are reading after the car has been idling that could be you problem
Thread Starter
Pro
Joined: May 2001
Posts: 524
Likes: 59
From: watchung N.J.
Re: Carb. experts (clem zahrobsky)
Thanks for all the tips guys, it is amazing how much we all can help each other here!, Anyway I called Holley tech line again ready to send the carb. back to them since no one there seemed to know more than I do or that gave a damn!
I finally got a hold of a old timer tech guy named "Ray" and he reallly went over every detail, I could'nt believe the difference of how much he really wanted to help me, and believe me this guy knows Holleys! Anyway he suggested opening up the secondary plate set screw .010" to allow more air to flow therefore carrying the fuel mixture more consistent at idle and low cruise speeds, I did this and then had to readjust the idle and idle mixture screws and you know, it really worked! I am not going to ask why, like many things on our vette, if it works pray to god that it will keep on working and move on to the next nightmare. Anyway I finally have consistent plugs all nice and light tan HOOOOOOOO-RAY! I know that was corny.
SPOKE- :cheers: :cheers: :cheers: :cheers: :cheers: :chevy :chevy
I finally got a hold of a old timer tech guy named "Ray" and he reallly went over every detail, I could'nt believe the difference of how much he really wanted to help me, and believe me this guy knows Holleys! Anyway he suggested opening up the secondary plate set screw .010" to allow more air to flow therefore carrying the fuel mixture more consistent at idle and low cruise speeds, I did this and then had to readjust the idle and idle mixture screws and you know, it really worked! I am not going to ask why, like many things on our vette, if it works pray to god that it will keep on working and move on to the next nightmare. Anyway I finally have consistent plugs all nice and light tan HOOOOOOOO-RAY! I know that was corny.
SPOKE- :cheers: :cheers: :cheers: :cheers: :cheers: :chevy :chevy
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Carb. experts (spokewrench)
spoke -
Sorry I didn't catch your post earlier - just now saw it. Looks like you got some good support and got the situation taken care of - good job!
I have seen several Holleys that have benefitted from cracking the secondary throttle open just a tad more than the spec. Once you've done it and have set the adjustment, it should hold quite well for you, so your fix should work well. Since your Holley does not have an idle metering circuit on the secondary side, you're leaning out the idle mixture by creating a controlled air bleed. The DP Holleys, as Clem states, are set up quite rich to avoid a secondary tip-in stumble, and this creates problems for many mild street engines as you've experienced.
It would still be a good idea to do a plug reading just like Clem states: Get a WOT run on the car and shut the engine off right away without letting the engine idle more than absolutely necessary. Take a plug reading and adjust main jets to correct as required. Once you have the main jets set up right, then work your idle circuit and manipulate with the secondary throttle cracking as required.
Sorry I didn't catch your post earlier - just now saw it. Looks like you got some good support and got the situation taken care of - good job!
I have seen several Holleys that have benefitted from cracking the secondary throttle open just a tad more than the spec. Once you've done it and have set the adjustment, it should hold quite well for you, so your fix should work well. Since your Holley does not have an idle metering circuit on the secondary side, you're leaning out the idle mixture by creating a controlled air bleed. The DP Holleys, as Clem states, are set up quite rich to avoid a secondary tip-in stumble, and this creates problems for many mild street engines as you've experienced.
It would still be a good idea to do a plug reading just like Clem states: Get a WOT run on the car and shut the engine off right away without letting the engine idle more than absolutely necessary. Take a plug reading and adjust main jets to correct as required. Once you have the main jets set up right, then work your idle circuit and manipulate with the secondary throttle cracking as required.
